Explore Swift Challenge #1

Euler Challenge

struct PrimeGenerator : Generator {
    typealias Element = Int

    private var myPrimes = [Int]() // store previous primes
    var current : Int = 2 // first prime is 2
    mutating func next() -> Int? {
        if myPrimes.count == 0 {myPrimes = [2]; return 2}
        NextNumber: while (current++ > 0) {
            for prime in myPrimes {
                // If a number has a prime factor it is not prime
                if current % prime == 0 {continue NextNumber}
            }
            myPrimes += current
            break
        }
        return current
    }
}

func factors(number : Int) -> [Int] {
    var myFactors = [Int]() // Resulting factors, may contain duplicates
    var myPrimes = PrimeGenerator() // On demand prime search
    var remainder = number // Portion remaining to factor
    var currentPrime = myPrimes.next()! // Pull out the first prime (2)

    while remainder > currentPrime {

        // Fetch all factors of the current prime
        while remainder % currentPrime == 0 {
            myFactors += currentPrime
            remainder /= currentPrime
        }

        // Move to the next prime
        currentPrime = myPrimes.next()!
    }

    // If the number is a prime itself, add it to the factor set
    if (remainder > 1) {
        myFactors += currentPrime
    }

    return myFactors
}

if (NSProcessInfo.processInfo().arguments.count < 2)
{
    println("Usage: \(NSProcessInfo.processInfo().arguments[0]) value-to-factor")
    Darwin.exit(-1)
}

var num : Int = NSProcessInfo.processInfo().arguments[1].integerValue
println(factors(num))

// Answer on 2011 Mac Mini: 0.012u 0.004s 0:00.01 100.0%	0+0k 0+0io 6pf+0w